1. Field of the Invention
The present application relates generally to an apparatus and method for bending a pipe and, more particularly, to an apparatus and method for introducing pressurized liquid into the interior of a pipe during bending to maintain the cross-sectional shape of the pipe.
2. Description of the Related Art
Vehicles powered by internal combustion engines, such as motorcycles, automobiles, snowmobiles, and all-terrain vehicles, for example, typically include an exhaust system to guide exhaust gases from one or more combustion chambers of the engine to the atmosphere. The exhaust system typically includes one or more exhaust pipes extending from the combustion chamber, or chambers, to a muffler of the exhaust system. A typical exhaust pipe is often circular in cross-section and can contain numerous bends throughout its length in order to tightly conform to the space available in such vehicles. It is generally desirable to maintain a consistent cross-sectional area and shape of the exhaust pipe in order to permit unobstructed flow of exhaust gases through the exhaust pipe. Changes in cross-sectional area or shape of the exhaust pipe tend to disrupt the flow of exhaust gases and/or partially reflect pressure waves, which can reduce the power output of the engine, especially at high engine speeds.
Commonly, exhaust pipes are fabricated by bending a generally linear, hollow workpiece around a circular die. However, when a tubular workpiece is bent, the outer side of the workpiece tends to collapse toward the inner side in the absence of internal support. That is, the cross-sectional dimension of the workpiece in a plane normal to the bending axis is reduced. Thus, the cross-sectional area of the exhaust pipe can also be reduced at the bent portion.
In order to provide support to an interior surface of the pipe, a mandrel can be introduced into the pipe. However, the mandrel must be capable of bending along with the pipe. In addition, due to a lengthening of the outer surface of the pipe, relative movement occurs between the pipe and the mandrel. Accordingly, a lubricant must be used to inhibit damage to the surface of the pipe due to movement on the mandrel. For environmental concerns, the lubricant typically must be reclaimed and the pipe subjected to additional cleaning process to remove residual lubricant, which increases manufacturing costs. Furthermore, despite the use of a lubricant, the mandrel can damage the surface and/or cross-sectional shape of the pipe.
In an alternative method, liquid is sealed within the pipe and pressurized during bending to provide support to the interior surface of the pipe. In such a method, the unbent pipe, or workpiece, is positioned horizontally on the bending apparatus. A first end of the pipe is received by a clamp, which includes an integral plug assembly, which is configured to creates a liquid tight seal with the first end of the pipe. A plug assembly is also inserted into the second end of the pipe and liquid is introduced into the interior of the pipe through the first plug. Once the interior of the pipe has been filled with liquid, the liquid is pressurized and an external force is applied to the pipe to bend the pipe around a die.